Then check out games 11-20, released (without absolute sales numbers) by NPD on Friday morning:

The Legend of Zelda: Spirit Tracks (DS, Nintendo)

New Super Mario Bros. (DS, Nintendo)

Mario and Sonic at the Olympic Winter Games (DS, Sega)

Mario and Sonic at the Olympic Winter Games (Wii, Sega)

Madden NFL 10 (360, Electronic Arts)

Scribblenauts (DS, Warner Bros.)

Mario Kart DS (DS, Nintendo)

Assassin’s Creed II (PS3, Ubisoft)

Madden NFL 10 (PS3, Electronic Arts)

Just Dance (Wii, Ubisoft)

I’ve brought this up before — in fact, apparently it was two years ago the first time I mentioned it — but analyst/blogger Bill Harris pointed out long ago that you can make a pretty good determination of how much gaming hardware will sell in November and December based on September and October’s sales.

Roughly speaking (and barring any outlying factors like price cuts or shortages), September and October are roughly similar, November is 2.5x September/October, and December is 3.75x September/October. This increase has everything to do with Christmas and nothing to do with anything else, which is why Sony’s Patrick Seybold’s comment on Thursday was pure spin: “It’s no surprise we’ve seen PS3 units sold every month nearly double since October.”

No, it’s no surprise at all, because Jesus’ birthday is the same day every year. PS3 sales doubled every month but so did sales of toasters, pencils and MadBalls.

Anything above and beyond the formula, though, is evidence that holiday promotions, marketing, etc. spurred demand even more than the usual holiday frenzy.

Note that the formula — while never perfect! — nailed the PSP and PlayStation 3 right on the nose. The Xbox 360 is low based on October’s numbers, but as Harris pointed out, 360’s October sales had an unexplained dip and were lower than September’s or November’s.

What did 360 sell in September? 352,600 units. What’s that times 3.75? Why, it’s 1.32 million.

So is there a point to all of this, besides Fun With Math? Yes: It illustrates just how seasonal Nintendo’s business is right now. Because Nintendo destroys the formula. This makes sense, because many the sort of casual gamers that Nintendo is targeting aren’t so bought in to the idea of gaming that they go out and buy games and hardware all year. Wii and DS were hot, hot Christmas gifts.

Wedbush Morgan Securities analyst Michael Pachter, in a note sent to investors on Friday, pointed out that the increased demand for Wii this year could be credited in part to a Wal-Mart promotion where consumers got a $50 gift card for buying Wii, which effectively lowered the price to a rock-bottom $150.

Nintendo, for its part, pointed out in its spin-letter that November and December sales were so high that they account for 18.7 percent of all Wii sales thus far in the U.S.

So can this month’s numbers please, please put the lie to the assertion that Wii’s hardware numbers are going to tank any day now? I don’t mean from comment posters and message board lurkers, who will never stop, but from actual industry pundits. I know that the number of Chicken Littles decreases every day when the sun rises and the sky has not yet fallen and a couple more of them come to the realization that, you know, it’s probably not going to. Yes, Wii sales will eventually decline, just like every game console. But it’s not happening on a shorter timeline.

Now, is everything rosy in Redmond? No. It’s still partially Nintendo’s fault that third parties can’t seem to have any smash successes on the level of New Super Mario Bros. But this is not to say that third parties are being blocked from succeeding on Wii. To look at the top 10, you’d think that third party software makers had been shut out. But looking down the list, you can see that some actually did very, very well on Wii. Did Sega stumble with MadWorld‘s sales? Sure, but it’s not crying about Mario and Sonic.

And look at Just Dance, up there at #20. Think about it: This $40 dancing game, well-promoted and featuring a great soundtrack, outsold every Ubisoft title not called Assassin’s Creed (and got within spitting distance of the PS3 version). Pachter, in his note, says that Ubisoft’s camera-based fitness game Your Shape was also a “big seller.”

In fact, Pachter’s comments give us a little more insight into third-party games that he was impressed with on Wii, as he points out that Drawn to Life: The Next Chapter and The Biggest Loser were “big sellers” for THQ (although both also have DS versions).

Analyst Jesse Divnich of EEDAR, in a note on Thursday, made what I think is the most cogent, cohesive argument about this situation that I’ve seen yet:

All too often the economy is blamed for the recent industry contraction. In reality, decreased sales in 2009 had more to do with a lack of innovation than economic recession. The growth of our industry now rests more on innovation than it ever has before, especially since non-traditional and casual markets consist of a larger share than in previous years. No longer can developers update a few maps, design some new weapons, add a few new characters, then throw a roman numeral at the end of the box and call it a “sequel”. That may work for core targeted games (Action, Shooters, and RPGs), but this strategy is not ideal for non-traditional and casual gamers.

Case in point: most sequels targeted to the mainstream and casual markets actually underperform in comparison to the original, which is the opposite to what has traditionally been the case for core targeted games. If you examine the Nintendo Wii and DS platforms (the current primary platform for this audience) Boom Blox outsold Boom Blox 2 (Wii); Brain Age outsold Brain Age 2 (DS); Guitar Hero III bested World Tour (Wii); The Bigs crushed The Bigs 2 (Wii); Mario & Sonic at the Olympics (Wii) is on track to outperform its Winter counterpart; Rayman Raving Rabbids (Wii) (2006) outsold its 2007 release; and lastly the original Cooking Mama(Wii, DS) (2006) has out sold all sequel versions combined.

EEDAR believes Nintendo understands the mindset of its consumers the best, which is why Nintendo rarely releases sequels within the same generation and, if they do, they are years apart. A good example of this is Mario Kart. Instead of releasing an annual Mario Kart title, Nintendo opts to only release one Mario Kart per hardware generation. Traditional thinking would assume that after an initial sales bump Mario Kart would simply just fade away on retail shelves—as so many others do. However, Nintendo realizes that if you can get an initial attachment rate on Mario Kart of 25% in 2008, they should be able to get the same attachment for new Wii purchasers in 2009 without having to release a sequel. To no surprise, the attachment rate for Mario Kart in 2009 was identical to that of 2008. Another example is Wii Fit. Whilst Nintendo did release a sequel to Wii Fit, The Wii Fit Plus (2009), the overwhelming majority of sales did not come from the stand-alone software edition, but rather the hardware/software bundle of the Wii Fit Plus. In other words the release of the expansion, which likely had minimal development costs, spurred sales of a 20 month old game wrapped in new packaging.

Of course this rule is not absolute for all casual and mainstream titles, some sequels do outperform the original, but in the overwhelming majority of cases, sequels on the Wii just cannibalize the potential sales of its predecessor. For reference, if the above examples were not proof enough, Call of Duty: World at War (2008) only outsold Call of Duty 3 by the smallest of margins and the most recent Call of Duty Modern Warfare: Reflex (2009) is currently on track to under-perform against World at War.

With the Wii making up the majority of the current casual and mainstream audience this finding should be carefully observed as Sony and Microsoft attempt to become more competitive in this space in future years.

So all you have to do is not release sequels? Unfortunately, it’s not that easy: All you have to do is nail it the first time. That’s harder. And unfortunately, this is not what many software makers seemed to be doing when they first approached Wii. Instead, the idea seemed to be: spend a little bit of money, make something barely acceptable — because screw ‘em, right, they’re casual gamers, they’ll play any old thing! — then follow up with a more polished sequel if it takes off.

Meanwhile, Nintendo keeps producing what are, by miles and miles, the most highly polished games on Wii. Third parties might not be able to have six million-sellers in a single month, it’s true. And, from where I’m standing, even great games like Boom Blox aren’t racking up the sales they deserve. But Divnich makes a compelling point: If software makers are not following the Nintendo-style model, they have very little room to complain that they’re not seeing Nintendo-style results.

Sony’s spin email was titled “2009: A Great Year For PS3,” which apart from being absolutely true is very carefully worded, because adding “and PSP” to that email subject would make it half a lie. 2009 was the year the PSP pretty much fizzled out, with few appealing games and very low hardware sales.

I’d expect to see a PSP2 announcement soon: Sony’s handheld business doesn’t need a shot in the arm. It’s already had plenty of shots and the nurse is having trouble finding a vein. It needs, I don’t know how to continue this metaphor, an enema. That’s terrible, I’m sorry. Sony needs to reboot its portable business. It needs a brand new platform, it needs a renewed commitment from all the major third parties, it needs a user experience that’s not frustrating and impossible. It needs the anti-PSP.

But 2009 was a great year for PS3, to be sure, as it’s drawn up relatively even with Xbox 360 in monthly sales, spurred on by the price drop and new model. The multiplatform games (by and large) are as good as the Xbox versions; the exclusive first-party stuff is much better.

For both PS3 and 360, Ubisoft’s assessment on Wednesday that it expects big software growth in the hard-core games category on these consoles in 2010 seems about right.

At this point in the lifecycle of the original Xbox, the Xbox 360 was already available. This console cycle is not going to end anytime soon, because nobody wants it to. Sony and Microsoft still have many more price points to which they can drop their consoles’ MSRPs. Third parties are just coming to grips with the realities of next-gen development and are in no hurry for next-next-gen.

How, then, to explain the year-over-year drop in sales for Xbox 360? While the strange days of this generation have illustrated that the game business is not a zero-sum one, it seems that PlayStation 3 and Xbox 360 may well be in large part fighting over the same group of people, and that gains on Sony’s side will accompany dips on Microsoft’s and vice versa.

So, with 2009 now fully behind us, what should we be looking for going into 2010?

I’m very interested at the prospect of getting to play with Sony’s and Microsoft’s motion controllers, but I don’t think either are going to generate even a tenth of the excitement or sales as Wii. That said, both are interesting, unique takes on the concept that will almost surely be an integral part of whatever new consoles that Sony and Microsoft do release, whenever that happens. If they’re truly amazing, they could at least generate a good deal of buzz around Xbox 360 and PlayStation 3.

How long will New Mario, Wii Fit Plus, etc. stay on the Top 10 every month? And once they’ve done their jobs, what else will Nintendo have to keep the mercurial masses entertained? Will the Vitality Sensor be the next Wii Fit or the next Wii Music?

Is it even possible anymore for Microsoft to break out ahead of Sony (or vice versa, come to think of it)? Or are they just going to be neck-and-neck until it’s time to start over again?

Finally, will Nintendo release Wii HD this year? (No.)

Special Note For Data Junkies: A few more tidbits from Pachter’s report that weren’t in NPD’s releases.

Guitar Hero: Van Halen sold “slightly less” than 75,000 units across all platforms.